Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-09-27
2004-10-26
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S193000, C526S194000, C526S204000, C526S205000, C526S220000, C526S224000, C525S256000, C525S261000
Reexamination Certificate
active
06809165
ABSTRACT:
The present invention relates to a process for the preparation of polymers having a narrow molecular weight distribution and a polymer prepared by the process.
Usually, polymers prepared by free radical polymerization of ethylenically unsaturated monomers have the disadvantage that the molecular weight of the polymer chains increases nonlinearly with the polymerization conversion and the polymer chains of the resulting polymer do not have a uniform molecular weight. The polymer obtainable by free radical polymerization therefore usually has a high polydispersity index PDI (PDI=M
w
/M
n
, where M
w
is the weight average molecular weight of the polymer and M
n
is the number average molecular weight of the polymer. This is due on the one hand to the half-lives of the free radical initiators, which may be from a few minutes to several hours. Consequently, the growth does not begin at the same time for all polymer chains, and it is for this reason that chains having different chain lengths form during the reaction. On the other hand, the growing polymer chains react with one another with combination or disproportionation, which leads to termination of chain growth. Since such termination reactions occur during the entire reaction time, this too leads to different chain lengths in the polymer.
In order to obtain polymers having a narrow molecular weight distribution, the growth of the chain should begin as far as possible at the same time for all polymer molecules and chain termination reactions should be suppressed.
WO 94/11412 describes a polymerization process for the preparation of a thermoplastic resin, a mixture of free radical initiator, a stable free radical and at least one polymerizable monomer being heated. Polymers having a narrow polydispersity are obtained. TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) and PROXY (2,2,5,5-tetramethyl-1-pyrrolidinyloxy) and derivatives thereof are proposed as stable free radical.
Further processes for the control of free radical polymerization, i.e. for the free radical polymerization in the presence of stable free radicals, are described in EP-A-0 735 052, U.S. Pat. No. 5,322,912, U.S. Pat. No. 5,412,047 and GB 1,124,009.
However, the processes described in said publications have the disadvantage that the polymerization takes place only very slowly and with unsatisfactory conversion in the presence of the stable free radicals.
EP-A-0 735 052 describes a polymerization process for the preparation of thermoplastic resins, in which specific sulfonic acid salts are concomitantly used for increasing the polymerization rate of the controlled free radical polymerization. 2-Fluoro-1-methylpyridinium p-toluenesulfonate is particularly preferably used. The sulfonic acid salts described are however not directly available and, owing to their fluorine content, are undesired in certain applications.
It is an object of the present invention to provide an alternative process for the preparation of polymers having a narrow molecular weight distribution, which process permits a higher reaction rate and higher conversions compared with known controlled free radical polymerizations.
We have found that this object is achieved by a process for the preparation of polymers, wherein at least one ethylenically unsaturated monomer is subjected to a free radical polymerization in the presence of stable free radicals or sources of free radicals and of a compound having at least one free thiol group to give a polymer, and wherein the molar ratio of compound having free thiol group to stable free radicals is from 0.05 to 1.1.
Surprisingly, it has been found that a substantial increase in the polymerization rate can be achieved by adding compounds which have at least one free thiol group, molecular weight control simultaneously being maintained. The compound having at least one free thiol group is used in an amount such that the molar ratio of compound having a free thiol group to stable free radical is from 0.05 to 1.1, preferably from 0.05 to 0.8, in particular from 0.1 to 0.7. At an amount below said range, no significant effect which increases the polymerization rate is observed. At an amount above said range no further rate increase occurs, and polymers having undesirably low molecular weights are obtained.
The polymers prepared by the novel process generally have a polydispersity index of from 1.1 to 5, preferably from 1.2 to 3.5, in particular from 1.3 to 2.5.
For carrying out the novel process, a reaction mixture which contains a stable free radical or a source of a stable free radical, at least one ethylenically unsaturated monomer and a compound having at least one free thiol group and, if required, a free radical initiator and, if required, solvents and/or conventional polymerization assistants is expediently heated to a high reaction temperature, for example from 40 to 200° C., in particular from 60 to 150° C. After reaction and cooling are complete, the polymer can be isolated and, if required, washed and dried. If the free radical formers described in more detail below are used as a source of the stable free radicals, the addition of a separate free radical initiator is superfluous. Alternatively, the free radical polymerization can also be thermally initiated in the absence of free radical initiators, in particular when vinylaromatic monomers, such as styrene, are used. Of course, mixtures of ethylenically unsaturated monomers may also be used.
The process is also suitable for the preparation of block copolymers. For this purpose, at least one second ethylenically unsaturated monomer is subjected to a free radical polymerization in the presence of the polymer obtained above. In a suitable procedure, the second ethylenically unsaturated monomer, which as a rule is different from the first ethylenically unsaturated monomer, is added to the polymer, which may have been isolated, if required with addition of fresh amounts of free radical initiator and free stable radicals, and the mixture is heated for polymerization. After cooling, a block copolymer is isolated and, if required, is washed and dried. Here, a second ethylenically unsaturated monomer is also to be understood as meaning a monomer mixture which is different from the first ethylenically unsaturated monomer with respect to the constitutive monomers or composition.
In order to obtain higher block copolymers, a third monomer may be added after polymerization of the second monomer and the polymerization may be carried out in the same manner. The isolation of the polymers formed as intermediates is advisable when a very high purity, well defined block limits and/or high homogeneity within the blocks are desired.
Suitable free radical initiators for the polymerization are in principle all compounds which are capable of initiating a free radical polymerization. Suitable free radical initiators are, for example, peroxides, hydroperoxides, peroxodisulfates, percarbonates, peroxoesters, hydrogen peroxide and azo compounds. Examples of initiators are hydrogen peroxide, dibenzoyl peroxide, dicyclohexyl peroxodicarbonate, dilauroyl peroxide, methyl ethyl ketone peroxide, di-tert-butyl peroxide, acetylacetone peroxide, tert-butyl hydroperoxide, cumyl hydroperoxide, tert-butyl perneodecanoate, tert-amyl perpivalate, tert-butyl perpivalate, tert-butyl perneohexanoate, tert-butyl perbenzoate, lithium, sodium, potassium and ammonium peroxodisulfate, azoisobutyronitrile, 2,2-azobis(2-amidinopropane) dihydrochloride, 2-(carbamoylazo)isobutyronitrile and 4,4-azobis(4-cyanovaleric acid). The free radical initiator may be both oil-soluble and water-soluble and are adapted to the chosen polymerization medium and to the chosen polymerization temperature in a manner known per se.
Suitable monomers polymerizable by the novel process are all those which have at least one ethylenically unsaturated group. The monomers may be used individually or as mixtures of one another. These monomers include olefins, in particular &agr;-olefins, e.g. ethylene and propylene, cycloalkenes, such as cyclohexene or norbornene, vinyla
Brinkmann-Rengel Susanne
Christie David
Haremza Sylke
Raether Roman Benedikt
BASF - Aktiengesellschaft
Teskin Fred
LandOfFree
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